1. Field of the Invention
The present invention relates to electrical cables. The invention relates, more particularly, to a novel coaxial cable structure and to flat coaxial cable assemblies comprising a plurality of such coaxial cables, as well as methods for manufacturing the same.
2. Description of the Prior Art
Flat coaxial cable assemblies are well known in the prior art. Generally, such cables include a spaced-apart, parallel and coplanar array of parallel, insulated signal wires. The signal wires are provided either with individual surrounding shield conductors or with a single shield common to all of the signal conductors. Usually, the shields consist of metal foil. In addition, in order to facilitate termination of the shields with electrical connectors, as well as the signal wires, it is usual to provide one or more drain wires which are in intimate electrical contact with the shield or shields. Thus, in cables wherein each signal wire is provided with its own shield, there will usually be a drain wire associated with each shield.
It has long been appreciated that in order to facilitate the termination of flat cables, particularly mass or gang termination of cables using automated installation tooling, it is necessary for all of the conductors at a stripped cable end to be located at predictable locations. This requirement is easily met in the case of simple, non-coaxial, flat cable where one is faced simply with a parallel, spaced array of wire conductors. In the case of flat, coaxial cable having drain wires, however, it has proven difficult to precisely locate both the signal and drain wires within the cable.
For example, in some prior art cable assemblies, the drain wires sprial around the associated signal wires. It is obvious that for any randomly chosen cross section of such a cable, the precise location of all of the drain wires cannot be predicted. Accordingly, cables of this variety cannot easily be terminated, except by hand.
In another type of flat, coaxial cable assembly, linear drain wires are provided which occupy precisely specified locations within the cable. Cable assemblies of this type are constructed by first manufacturing the individual coaxial cables which make up the assembly and then embedding the cables in a common dielectric matrix. Each individual coaxial cable is made by placing an insulated signal wire and an uninsulated drain wire in parallel alignment and then wrapping the wire pair in a metal foil shield. The completed coaxial cables are placed in the assembly in such a way that all of the signal and drain wire pairs are similarly oriented, thus making the location of each predictable. It will be appreciated, however, that cable assemblies of this type are difficult to manufacture because it is possible for the drain wire in each coaxial cable to migrate underneath the foil shield, with such migration being a particularly acute problem during the step of foil wrapping itself. Of course, if a drain wire does move in this way during manufacture, it will not occupy its assigned location in the cable assembly.
In view of the foregoing description of the state of the art, it is clear that there is a need for a flat, flexible, coaxial cable assembly in which all conductors are located at predictable locations, in order to facilitate termination, and which may be easily and simply manufactured.
The objects of the present invention, are, accordingly, to provide such a cable assembly, as well as methods for manufacturing the same.